When someone shoots someone else in front of witnesses, the police tend to interview suspects and witnesses to the shooting almost immediately. There are good reasons for that. Eyewitness memory begins to blur almost immediately, then continues to fade over time. As for suspects, the police want them to commit to a story early, before they can come up with a narrative that clears them of blame.

But when a police officer pulls the trigger, the officer is often given a “cooling-off period” before he is asked to give a statement. Any other police officers who might have witnessed the shooting are also sometimes given time to “cool off.”

The discrepancy arises from the unlikely but popular and persistent theory that while the memories of regular people tend to degrade over time, the memories of police officers somehow improve after they’re given a few days to ruminate. A cynic might point out that this theory also gives the officers involved some time to collaborate on a story.

A new study of 87 veteran police officers, some interviewed immediately after active-shooter training and some two days after the training, could start to change that thinking. “We did not find any evidence,” wrote criminologists Geoff Alpert, Louise Porter and Justin Ready, “that delay improves either recall or cognitive capability that could indicate enhanced ability to respond to questioning.”

Even though officers who were questioned shortly after emerging from a high-stress scenario “felt heightened anxiety, and reported less confidence in their cognitive ability,” the study found that those factors “did not seem to impede officers’ ability to recognize details of the scenario, or form new memories and perform in the cognitive tasks.” …

The study also built on a commonly held perception about memory. “One of the most fundamental laws of memory,” said Stanford professor Elizabeth Loftus, a renowned expert on human memory, “is that it fades over time.” She noted that memory “not only fades, but is also vulnerable to post-event contamination, or eroding.” Loftus said that “we couldn’t see any good reason for this kind of long delay” in conducting police interviews.

This isn’t the first study to reach that conclusion. In 2014, I wrote about a similar study by Alpert and Jeff Noble, a former deputy chief with the police department in Irvine, Calif. That study, too, found no advantage to a “cooling-off” period: “The officers reporting on the threat immediately after it occurred had sharper recollections than those who shared their memories only after a few days had passed,” and “asking them to relay facts immediately after an event may provide the best results for threat-related variables.”

That study also noted the contrast between investigations of officer-involved shootings and shootings not involving police officers.

Investigators ask for the cooling off period for officers, but not for any other citizen equally impacted by such a stressful event. Indeed, in the case of a shooting involving one dead person and another holding a gun, only an officer may avoid immediate arrest for refusing to explain the events leading to the death …

The manner in which an agency investigates its own, especially after a shooting incident, directly impacts the public trust. People have concerns of corruption because of the powers held by officers and the potential for abuse, and well-documented instances exist of excessive force at the hands of unprincipled officers. This public trust concern becomes heightened because police officers frequently face investigation by their own agencies, which may have an interest in protecting personnel from criticism and liability, thus, enhancing their reputation or avoiding financial damages.

In fact, from what I can tell, there isn’t really much disagreement here at all. The “other side” on this issue — the side that claims that police officer memories improve after a few days — is really just one guy. His name is Bill Lewinski, and he runs an organization called the Force Science Institute.

From Jackman’s article:

Bill Lewinski of the Force Science Institute is regarded by many police officials as the definitive expert on the subject of interviewing officers after shootings. He is a behavioral scientist who has studied police use-of-force issues since 1975. “Delay enhances an officer’s ability to more accurately and completely respond to questions,” he wrote in one widely cited paper, arguing for “a recovery period of at least 48 hours before being interviewed in depth.”

He was critical of the Alpert group’s paper, which was first previewed at a national police chiefs’ conference and is being reviewed for publication. Lewinski said that he had interviewed more than 2,000 officers who had been involved in shootings and that “their reactions are all over the place.” But he said that experts “will tell you, no question, if you need to improve memory, sleep on it.” Lewinski said there were “serious flaws in the current research. The best study has not been done.” …

Attorney Edward J. Nuttall, who has represented dozens of officers involved in shootings, said: “Based on my experience, the memory is no better or worse immediately after, whether it’s three or six days after the incident. What is much different is their physical self. Their blood pressure, the adrenaline, the ability to articulate what they did or what they observed. Dr. Lewinski’s the authority on this. It’s common knowledge that after three or four sleep cycles, your adrenaline will go down, your blood pressure will go down, and you’re better able to articulate what you’ve observed.”

It’s true that a cop who has had sufficient sleep before a shooting will recall it better than a cop who hasn’t. But that’s different from what Lewinski claims: that cops will recall a shooting better after they’ve had a night’s sleep than they will immediately after. Nearly all the research on memory shows that we quickly forget vast amounts of the information we take in. In fact, there has been so much research in this area that we can document just how much information we lose over time with a “forgetting curve.” Without repetition of the information, within an hour or so, we lose about 20 percent of what we’ve learned. After a day, we retain less than 40 percent. After two days, it’s less than 20 percent. As far as I know, there is no research not written by Lewinski that supports a “police officer exception” to this problem.

Research into cognitive bias has given us lots of other reasons to interview police officers as soon as possible. For example, we know that most people tend to remember controversial events in ways that make themselves look as good as possible, a phenomenon known as self-serving bias or egocentric bias. There’s also a concept called fading affect bias, which causes us to forget memories that bring negative emotions and retain memories that invoke positive ones. One study estimated that this particular bias can take effect in as quickly as 12 hours. Which means that in a close-call shooting, the further we get from the event itself, the more likely the police are to recall only those details that justify the shooting.

Researchers have found another bias called mood-state dependent retrieval, which posits that we’re more likely to remember things in more detail when we’re in a similar mood as we were when the event in question occurred. This means that waiting until the officers’ adrenaline subsides and their blood pressure drops may inhibit their ability to recall a shooting accurately. And then there’s memory conformity, which describes how if allowed to consult with one another, multiple witnesses to the same event will begin to influence how each witness remembers the event individually. This is why it’s a bad idea to let police officers consult with one another after a shooting. (And again, it’s a concept that police departments seem to understand pretty well when interviewing eyewitnesses to shootings not involving cops.)

And all of that is just the unintentional bias that can corrupt how we recall a traumatic event. “Cooling-off periods” also give corrupt cops ample opportunity to consult with one another, consult with attorneys and consult with corrupt internal affairs investigators to reconstruct shootings to exonerate themselves. No, not all cops do this. But we’ve documented plenty of examples of it here at The Watch.

Nuttall’s assertion that Lewinski is “the authority on this” is utter nonsense. Lewinski isn’t some neutral researcher looking for the truth. Here’s an excerpt from a 2015 profile in the New York Times:

Dr. Lewinski says his research clearly shows that officers often cannot wait to act.

A former Minnesota State professor, he says his testimony and training are based on hard science, but his research has been roundly criticized by experts. An editor for The American Journal of Psychology called his work “pseudoscience.” The Justice Department denounced his findings as “lacking in both foundation and reliability.” Civil rights lawyers say he is selling dangerous ideas …

Many policing experts are for hire, but Dr. Lewinski is unique in that he conducts his own research, trains officers and internal investigators, and testifies at trial. In the protests that have followed police shootings, demonstrators have often asked why officers are so rarely punished for shootings that seem unwarranted. Dr. Lewinski is part of the answer . . .

Dr. Lewinski said he was not trying to explain away every shooting. But when he testifies, it is almost always in defense of police shootings. Officers are his target audience — he publishes a newsletter on police use of force that he says has nearly one million subscribers — and his research was devised for them. “The science is based on trying to keep officers safe,” he said.

Dr. Lewinski, who grew up in Canada, got his doctorate in 1988 from the Union for Experimenting Colleges and Universities, an accredited but alternative Cincinnati school offering accelerated programs and flexible schedules. He designed his curriculum and named his program police psychology, a specialty not available elsewhere …

… In separate cases in 2011 and 2012, the Justice Department and a private lawyer asked Lisa Fournier, a Washington State University professor and an American Journal of Psychology editor, to review Dr. Lewinski’s studies. She said they lacked basic elements of legitimate research, such as control groups, and drew conclusions that were unsupported by the data.

“In summary, this study is invalid and unreliable,” she wrote in court documents in 2012. “In my opinion, this study questions the ability of Mr. Lewinski to apply relevant and reliable data to answer a question or support an argument.”

Lewinski is an unapologetic partisan who pushes pseudoscience in order to clear cops of wrongdoing. He thinks cops today wait too long before using deadly force. It’s bad enough that he is asked to provide training to police departments across the country. Or, worse, that they hire him to train officers on how to conduct internal investigations after lethal force has been used. In fact, I can recall three different occasions in which I’ve read about a reform-minded police chief or DA — someone I interviewed for a story about a separate issue — who then went on to hire Lewinski to conduct lethal force training. I contacted two of them after the fact, and both said they weren’t aware of the criticisms of Lewinski.

But it’s more damning still that our system regularly allows someone like Lewinski to testify as an expert witness. It’s regrettable, but understandable, that police departments might hire someone with Lewinski’s pro-police views to conduct training. But the courts are supposed to be neutral. Letting Lewinski testify as a certified “expert witness” sends the message to jurors that both he and the opposing witness — perhaps someone like Alpert or Noble — are of roughly equal credibility, and should be given equal consideration, even though that’s just not true. And when opposing experts testify in the same trial, jurors tend to be persuaded by things other than the robustness of their expertise — things like likability, how much they were paid, or how well they speak. It’s another example of how the courts have neglected their duty as the gatekeepers of scientific evidence and expert testimony.

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Radley BalkoRadley Balko writes and edits The Watch, a reported blog covering civil liberties and the criminal-justice system. Previously, he was an investigative reporter for the Huffington Post and a writer and editor for Reason magazine. His most recent book is "The Cadaver King and the Country Dentist: A True Story of Injustice in the American South." Follow